PuTTY is a client program for the SSH, Telnet and Rlogin network protocols.

These protocols are all used to run a remote session on a computer, over a network. PuTTY implements the client end of that session: the end at which the session is displayed, rather than the end at which it runs.

In really simple terms: you run PuTTY on a Windows machine, and tell it to connect to (for example) a Unix machine. PuTTY opens a window. Then, anything you type into that window is sent straight to the Unix machine, and everything the Unix machine sends back is displayed in the window. So you can work on the Unix machine as if you were sitting at its console, while actually sitting somewhere else.

* Kerberos/GSSAPI authentication in SSH-2.* Local X11 authorisation support on Windows. (Unix already had it, of course.)* Support for non-fixed-width fonts on Windows.* GTK 2 support on Unix.* Specifying the logical host name independently of the physical network address to connect to.* Crypto and flow control optimisations.* Support for the zlib@openssh.com SSH-2 compression method.* Support for new Windows 7 UI features: Aero resizing and jump lists.* Support for OpenSSH AES-encrypted private key files in PuTTYgen.* Bug fix: handles OpenSSH private keys with primes in either order.* Bug fix: corruption of port forwarding is fixed (we think).* Bug fix: various crashes and hangs when exiting on failure,* Bug fix: hang in the serial back end on Windows.* Bug fix: Windows clipboard is now read asynchronously, in case of deadlock due to the clipboard owner being at the far end of the same PuTTY's network connection (either via X forwarding or via tunnelled rdesktop).